1. Field of the Invention
The present invention relates to a time delay switch. In particular, the present invention relates to switches that turn on or turn off the power to an electrical load at preselected, adjustable intervals of time after the switch is thrown.
2. Discussion of Background
Time delay circuits are frequently used to turn lights and other electrically-powered devices on or off, for example, to ensure that garage lights or bathroom lights are turned on while the operator is leaving the area, and automatically shut down after a preselected interval of time or at a subsequent, specific time. Time delays may also be convenient when using other appliances such as fans, air conditioners, humidifiers, electric space heaters, etc. A time delay circuit can be built into an appliance or wall outlet, or connected in the circuit through which electrical power is supplied to the appliance.
Many types of time delay circuitry are available, all providing for automatic control of a circuit so that lights or other electrical loads are turned on or off after a preselected time interval. By way of example, Dalton (U.S. Pat. No. 5,501,607) uses a single pole switch that is toggled "on" for a moment before being toggled "off." The short "on" period signals that automatic delay is desired and power flows through the circuit load for a preselected time limit. Hochstein, et al. (U.S. Pat. No. 4,500,795) automatically shut off a circuit using digital logic. Their device alerts the user to the fact that the delay period is almost over by briefly turning off a light (or other load) just before it is permanently turned off. The device includes a momentary push-button type switch and a set-reset circuit that resets the delay each time the switch is pressed. Coker (U.S. Pat. No. 4,494,012) discloses an automatic delay circuit with a three-position switch: ON. OFF, and TIMER. The time delay switches described by Jabor (U.S. Pat. Nos. 4,389,599 and 4,339,696) delay the turning off of a light after the switch has been moved to the "off" position. Both designs enable varying the duration of the delay interval by changing the resistance of a variable resistor.
Several devices simply delay the turning off of electrical power after the on/off switch is moved to the "off" position. These include Mendelson (U.S. Pat. No. 4,382,192); Dandrel, et al. (U.S. Pat. No. 4,101,811), a circuit that receives less power at some point during the delay interval; and Moroto, et al. (U.S. Pat. No. 3,819,885), a mechanical clock to determine the length of the delay.
Despite the many known time delay switches that are available, there is a need for a simple, low cost, time delay switch that allows the user to set a preselected but variable delay time. The switch should be easy to use when needed, and preferably be configured for direct replacement of conventional wall-mounted switches.